Casting metals

ABSTRACT

The casting of metals or salt and products made by casting metals or salts are described. For example, a method for casting metals or salts includes evacuating a mold that is pressurized with an inert gas and coupled to a pressurized source of molten metal or salt, wherein the pressurization of the source is sufficiently high to drive the molten metal or salt into the mold in response to the evacuation.

BACKGROUND

This invention relates to processes for casting metals and the resultingproducts.

In metalworking, casting is process in which molten metal is added to amold (also known as a tool or a die) that defines a hollow cavity. Themolten metal is then allowed to cool and solidify. The solid casting isthen removed from the mold. If the casting is to have a relativelycomplex geometry (e.g., with holes, undercuts, and/or integratedchannels) cores and/or multi-slide techniques can be used. Castings canbe used to create a variety of different products.

SUMMARY

The casting of metals and products made by casting metals are described.For example, a method for casting metals or salts includes evacuating amold that is pressurized with an inert gas and coupled to a pressurizedsource of molten metal or salt, wherein the pressurization of the sourceis sufficiently high to drive the molten metal or salt into the mold inresponse to the evacuation.

This and other methods can include one or more of the followingfeatures. Evacuating the mold can include coupling the mold to a vacuumchamber, e.g., wherein the vacuum chamber has a volume that is 30 or 50times a volume of the mold. The source of molten metal or salt can bepressurized to a pressure of less than 0.2 MPa gage or less, e.g., toabout 0.1 MPa gage. The source of molten metal or salt can bepressurized with the inert gas. The molten metal or salt is one ofcopper, steel, aluminum, alloys, salt or salt mixtures. The mold can beconfigured to cast a coil, for example, a coil as described in thisapplication. The mold can be evacuated, e.g., in 0.1 seconds or less. Insome implementations, prior to the evacuation, the pressurization of themold and the pressurization of the source are comparable and moltenmetal or salt is exposed to the inert gas pressurizing the mold. Themold can include a core, multiple slides, or both a core and multipleslides. The mold can include a gas-permeable core. Evacuating the moldcan include evacuating at least part of the mold by drawing gas throughthe gas-permeable core. The pressurized source can include a cruciblethat includes resistive or inductive heating elements integrated thereinor disposed along a surface thereof.

As another example, a coil includes a cast unitary metal strip coveredby an insulator and layered to form a plurality of turns about an axis,the metal strip having a width generally perpendicular to the axis and aheight generally parallel to the axis, wherein the width is larger thanthe height.

This and other coils can include one or more of the following features.The cast unitary metal strip can have a generally rounded rectangularcross-section parallel to the axis. The insulation of adjacent turns ofthe metal strip contact each other over substantially the entire widthof the metal strip. The coil can display physical characteristics thatare characteristic being cast in a relatively low pressure differencecasting process, for example, wherein the physical characteristics isdimensions of microbubbles in the coil. The coil can display physicalcharacteristics that are characteristic being cast directly in a shapethat is nearly suitable for use. For example, a the metal strip can befree from stress-induced microdefects resulting from an application of aforce perpendicular to the axis to shape the metal strip. The metalstrip can include aluminum and the insulator can include aluminum oxide.The metal strip can include copper. The cast unitary metal strip coilcan have a generally trapezoidal cross section parallel to the axis,wherein the cross section is oriented to intersect comparable crosssections of other coils of a motor or generator arranged generallyconcentrically about a center. The generally trapezoidal cross sectioncan be formed by a single winding of the cast unitary metal strip. In atleast one cross section parallel to the axis, regions of the castunitary metal strip can have non-uniform widths. For example, theregions progressively increase or decrease in width along the axis. Inthe at least one cross section parallel to the axis, regions of the castunitary metal strip can have non-uniform heights, for example, whereinthe regions can progressively increase or decrease in height along theaxis. The coil can be cast in an extended shape that forms a pluralityof turns about an axis with a space between adjacent turns. For example,the space between adjacent turns can be 5 to 10 times wider than thethickness of the metal strip along the axis. In some cases, the spacebetween adjacent turns can be, e.g., 1 to 20 mm.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a casting system.

FIG. 2 is a schematic representation of the casting system in thecasting process.

FIG. 3 is a schematic representation of a conductive coil that can becast using, e.g., the casting system of FIGS. 1 and 2.

FIG. 4 is a schematic representation of one possible cross-section ofthe conductive coil of FIG. 3.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a schematic representation of a casting system 100. Castingsystem 100 includes a crucible 105, a crucible pressure container 110, acasting mold 115, a feed pipe 120, a pressurized inert gas source 125,and a vacuum chamber 130. Feed pipe 120 extends into crucible 105 andforms a fluid flow path suited for pressure-driven flow of moltenmetal(s) 135 from crucible 105 into the interior 117 of mold 115. Moltenmetal(s) 135 can be, e.g., aluminum, magnesium, zinc, copper, iron, ortheir alloys, including steel. Mold 115 can be selected based on themetal(s) 135 to be cast and can be, e.g., a steel or sand die. In someimplementations, ceramic molds can be used. In some implementations,cores and sliders can be used. For example, the cores can be permanentor non-permanent. Casting system 100 can be operated to drive metal(s)135 from crucible 105 through feed pipe 120 into the interior volume 117of mold 115 using a relatively low pressure differential.

Gas source 125 can contain a relatively high pressure inert gas such asnitrogen or a noble gas. In some implementations, the inert gas can bedried. Gas source 125 can be, e.g., a pressurized gas canister or line.Gas source 125 is coupled to one or both of the interior volume 117 ofcasting mold 115 and the interior volume 112 of crucible pressurecontainer 110 via one or more lines 140, 145. Lines 140, 145 can beopened and closed using one or more valves 150, 151. As discussedfurther below, gas source 125, lines 140, 145, and valves 150, 151 areconfigured to pressurize the interior volume 117 of casting mold 115 andthe interior volume 112 of crucible pressure container 110 atapproximately the same rate.

As discussed further below, line 145 is dimensioned and gas source 125is able to provide a sufficient volume flow of inert gas to rapidly fillthe interior volume 112 of crucible pressure container 110. For example,in some implementations, line 145 and gas source 125 are able to fillthe interior volume 112 of crucible pressure container 110 in less than1 sec. In general, interior volume 112 can be filled without associatedturbulence in the metal bath. To assist in rapid filling, valve 151 isgenerally positioned immediately adjacent the interior volume 112 ofcrucible pressure container 110. With such a positioning, the volume ofline 145 between valve 151 and interior volume 112 is relatively smalland the rate of pressure change in interior volume 112 is increased.

In some implementations, the interior of crucible pressure container 110can be tailored to conform to the exterior of crucible 105. For example,in some instances, the exterior of crucible 105 can be generallycylindrical or conical in shape, and the interior of crucible pressurecontainer 110 can define a generally cylindrical or conical volume thatconforms to the exterior of crucible 105 with a small tolerance. Such atailoring can reduce the size of interior volume 112 and speed changesin pressure.

In some implementations, resistive or inductive heating elements can beintegrated into crucible 105, integrated into crucible pressurecontainer 110, and/or disposed along a surface of either. Such heatingelements can facilitate reductions in the size of interior volume 112.

Vacuum chamber 130 is coupled to the interior 117 of casting mold 115via a line 155. Line 155 be opened and closed using one or more valves160. Vacuum chamber 130 has a volume that is significantly larger thanthe volume of the interior 117 of casting mold 115. For example, thevolume of vacuum chamber 130 can be 50 or more times the volume of theinterior 117 of casting mold 115. Valve 160 can be a quick acting valve,e.g., a valve that can complete the transition from a closed state to anopen state in less than 100 milliseconds.

As discussed further below, line 155 is dimensioned and chamber 130 isable to withdraw a sufficient volume flow of inert gas to rapidly emptythe interior 117 of casting mold 115. For example, in someimplementations, line 155 and chamber 130 are able to empty the interior117 of casting mold 115 in under 0.1 seconds. To assist in emptying,valve 150 is generally positioned immediately adjacent the interior 117of casting mold 115. With such a positioning, the dead volume of line140 between valve 150 and interior 117 is relatively small and little orno additional air must be withdrawn through line 155. Also, valve 160 isgenerally positioned immediately adjacent the interior 117 of castingmold 115.

In implementations where casting mold 115 includes a sand core or othergas-permeable core, line 155 can be coupled to withdraw gas through asolid (but gas-permeable) portion of the core. This would allow gas tobe withdrawn from the entire casting volume of mold 115, as well asavoid gas emissions from the core.

In some implementations, the interior 117 of casting mold 115 iscoupled, e.g., to atmosphere via one or more lines 165. In theillustrated implementation, line 165 includes a check valve 170 thatonly allows unidirectional flow out of the interior of casting mold 115.In other implementations, one or more lines 165 can be unobstructed andun-valved passages that allow relatively small flow rates compared tothe flow rates through lines 140, 155 when one or more of valves 150,160 is open.

In preparation for casting, casting mold 115 and crucible pressurecontainer 110 are filled with inert gas from gas source 125, with thepressures in casting mold 115 and crucible pressure container 110ultimately rising above atmospheric pressure. For example, casting mold115 and crucible pressure container 110 can be pressurized to 1 MPagage, although generally casting mold 115 and crucible pressurecontainer 110 2will be pressurized to 0.2 MPa gage or less. For example,casting mold 115 and crucible pressure container 110 can ultimately bepressurized to 0.02-0.08 MPa gage. The pressurization process can insurethat reactive gases (e.g., atmospheric oxygen) do not remain in castingmold 115 and crucible pressure container 110 during casting. Forexample, relatively pure inert gas can flow from gas source 125 intocasting mold 115 and crucible pressure container 110 at the same timethat a mixture of inert gas and reactive gases escapes from casting mold115 and crucible pressure container 110 through one or more lines 165.Depending upon the respective flow rates and volumes, the reactive gasesin casting mold 115 and crucible pressure container 110 will eventuallybe depleted and the gas in casting mold 115 and crucible pressurecontainer 110 will have a composition that resembles the composition ofthe gas from gas source 125.

Before, during, and/or after casting mold 115 and crucible pressurecontainer 110 are filled with inert gas, crucible 105 can be heated tomelt metal(s) 135. Feed pipe 120 extends into the molten metal(s) 135 incrucible 105. As or after metal(s) 135 melts, the pressures of theinterior 117 of casting mold 115 and the interior 112 of cruciblepressure container 110 can be regulated to form a head 175 of moltenmetal(s) 135 that fills the gating system of casting mold 115. In theillustrated implementation, molten metal(s) 135 rises to a level 180that is slightly below portion of casting mold 115 where the finalproduct is to be cast. In some implementations, feed pipe 120 include aheating system to control the temperature of molten metal(s) 135 in feedpipe 120 (not shown).

The particular approach for regulating the pressures in casting mold 115and crucible pressure container 110 can depend upon the particularstructure of casting system 100. For example, in some implementations,the pressures in casting mold 115 and crucible pressure container 110may inherently result from the respective flow rates through lines 140,145, and 165. For example, the sizes of lines 140, 145, and 165 can beselected so that the escape of gas from casting mold 115 through line165 results in the pressure of casting mold 115 being lower than thepressure in crucible pressure container 110 by a desired amount. Otherimplementations—including implementations that include pressure sensorsand active feedback control—are possible.

In general, casting mold 115 will be heated to a temperature suitablefor good form filling behavior and a minimum fatigue fretting of thedie. For example, when copper is being cast, permanent casting mold 115will be heated to temperatures between 100-350° C. In contrast, whenaluminum is being cast, permanent casting mold 115 will be heated totemperatures between 250-350° C.

FIG. 2 is a schematic representation of casting system 100 in thecasting process. With casting mold 115 and crucible pressure container110 both pressurized, valve 150 is closed and valve 160 opened. Sincevacuum chamber 130 has a volume that is significantly larger than thevolume of the interior 117 of casting mold 115, pressure in the interior117 of casting mold 115 falls nearly to zero very rapidly. For example,the pressure in the interior 117 of casting mold 115 can fall nearly tozero in under 0.1 seconds. In contrast, crucible pressure container 110remains pressurized, and the head 175 of molten metal(s) 135 rises to alevel 185, filling casting mold 115.

As discussed above, the pressure in casting mold 115 and cruciblepressure container 110 can, in some implementations, be 0.1 MPa or soabove atmospheric pressure. In the context of casting metals, this is arelatively low pressure difference, i.e., around two atmospheres. By wayof contrast, high pressure die casting can be performed at pressures upto, e.g., 120 MPa or so, i.e., around 120 atmospheres pressuredifference.

At such high pressures, the velocity of molten metals in the castingmold reaches a high velocity, e.g., 200 m/s.

By operating at such a relatively low pressure, the present castingprocess is both safer and quicker. Indeed, a relatively low pressurecasting process may not be subject to stringent regulatory requirements.Also, the melt need never be exposed to an oxidative atmosphere. Rather,the melt is exposed only to an inert atmosphere and (essentially)vacuum.

In some instances, products cast using such a relatively low pressuredifference may display physical characteristics that are characteristicof the casting process. For example, in some instances, products may beless likely to include microbubbles than products that are cast usinghigh pressure casting. In high pressure casting, any gas trapped in themolten metal will expand significantly once the high casting pressure isreleased. In contrast, with a relatively low pressure casting, thevolume expansion of gas in the molten metal is significantly smaller.

As another example, in some instances, products cast using such arelatively low pressure difference may display surface structuringcharacteristic of the casting process.

In some implementations, during or after the evacuation of the interior117 of casting mold 115, the pressure applied to molten metal 135 can beincreased. For example, in some implementations, an additional source ofpressurized inert gas can be coupled to the interior 112 of cruciblepressure container 110 by a valve/line system (not shown). Such a valvecan be opened in response to the opening of valve 160 to increase thepressurization in interior 112 of the interior volume 112 of cruciblepressure container 110. As another example, in some implementation,interior volume 112 of crucible pressure container 110 can bepressurized through valve 151. In either case, pressurization ofinterior volume 112 combined with evacuation of the interior 117 ofcasting mold 115 can increasing filling speed and the mass inertia,allowing smaller wall thicknesses in the casting.

The casting process illustrated schematically in FIGS. 1 and 2 can beused to cast a variety of different products—including products that aredifficult to cast using other casting techniques.

FIG. 3 is a schematic representation of a conductive coil 300 that canbe cast using, e.g., casting system 100. Conductive coil 300 is aunitary cast piece that can be used, e.g., in a motor or an electricgenerator. The surface of metal strip 310 is covered with a relativelythin insulator so that metal strip 310 forms a coil-shaped conductivepath.

Conductive coil 300 defines a gap 305 around an axis 307 about which ametal strip 310 is “wound” in a series of layers 312 that each form aturn of coil 300. Metal strip 310 has a height 315 that is less than awidth 320, where width 320 is oriented generally perpendicular to axis307 and height 315 is oriented generally parallel to axis 307. Asdiscussed in further detail below, the dimensions of metal strip 310 aregenerally not be uniform—either within a single layer 312 or from onelayer 312 to another layer 312. In the illustrated implementation, metalstrip 310 is generally rectangular in cross-section with generally flatinsulated surfaces of adjacent layers 312 in contact with one another.This is not necessarily the case. For example, in some implementations,the surface of metal strip 310 may be intentionally structured, e.g., sothat adjacent layers 312 engage with one another to increase the area ofcontact.

Although layers 312 in conductive coil 300 are shown in the schematicrepresentation as having generally sharp edges 325 and gap 305 is shownas having a cuboid shape, in general, both edges 325 and the edges ofgap 305 will be at least somewhat rounded. Further, although thecross-sectional area of metal strip 310 is illustrated as generallyrectangular with sharp edges, this is generally not the case.

Conductive coil 300 can be cast from one or more metals, includingaluminum, copper, manganese, or steel. Conductive coils cast fromaluminum are lighter that comparably dimensioned conductive coils castor otherwise formed from copper. The insulator can be formed from one ormore layers of different materials and can include, e.g., metal oxidessuch as aluminum oxide.

In some implementations, conductive coil 300 can be cast directly in ashape that is nearly suitable for use, e.g., in a motor or generator. Inother implementations, conductive coil 300 can be cast in an extendedshape that forms a plurality of turns about axis 307 but must becompressed along the direction of axis 307 prior to use. For example,the space between adjacent turns can be 5 to 10 times wider than thethickness of the metal strip along the axis. In some cases, the spacebetween adjacent turns can be, e.g., 1 to 20 mm. Regardless of whethercoil 300 is cast in an extended shape or in a shape that is nearlysuitable for use, it is not necessary to bend or otherwise shape metalstrip 310 by applying a force perpendicular to axis 307, e.g., to windmetal strip 310 about a bobbin. The physical structure of metal strip310 may be characteristic of such a casting. For example, whenconductive coil 300 is cast directly in a shape that is nearly suitablefor use, metal strip 310 may maintain this nearly suitable shape withoutthe application of external forces. As another example, the surface ofmetal strip 310 may be free from stress-induced microdefects associatedwith such a shaping by application of forces perpendicular to axis 307.

FIG. 4 is a schematic representation of one possible cross-section ofconductive coil 300. The cross-section—which is generally parallel toaxis 307 and arranged to cut through a concentric arrangement ofcoils—cuts across metal strip 310 of coil 300 at different regions 405,410, 415, 420, 425, 430, 435, 440.

In the illustrated implementation, coil 300 is dimensioned to fill alarge percentage of the design space of an electric motor or generatorwithin the illustrated cross-section with a single metal strip. In moredetail, a motor or generator can include several coils arrangedconcentrically, for example, mounted on a stator disposed around arotor. In the perspective of FIG. 4, the coils would be arrangedconcentrically about a center that is positioned below coil 300.Additional coils would thus be positioned, e.g., below and to the leftand right of coil 300, oriented so that their respective axes aredirected to the center of the concentric arrangement. With such adisposition, less space is available for each coil toward the center ofthe concentric arrangement than is available to toward the outside ofthe concentric arrangement.

Motor and generator coils generally have a trapezoidal cross sectionthat is narrower on the side which is to be disposed toward the centerof the concentric arrangement and wider on the side which is to bedisposed toward the outside of the concentric arrangement. In coilsformed by winding a wire around a bobbin or other member, such atrapezoidal cross section is generally achieved by winding the wire moretimes toward the outside of the concentric arrangement than toward thecenter of the concentric arrangement.

In contrast, coil 300 can be dimensioned to have a trapezoidal crosssection with a single metal strip wound about axis 307. Thisdimensioning is reflected in the non-uniform sizing of regions 405, 410,415, 420, 425, 430, 435, 440. For example, region 420 has a width 445that is smaller than a width 450 of region 405. Regions 410, 415 havewidths that are intermediate to widths 445, 450. Similarly, region 440has a width that is smaller than the width of region 425, with regions430, 435 having intermediate widths.

In some implementations, the height of regions 405, 410, 415, 420, 425,430, 435, 440 can also be non-uniform. For example, a height 455 ofregion 425 can be less than a height 470 of region 440. Regions 430, 435can have heights 460, 465 that are intermediate to heights 455, 470.Similarly, region 405 can have a height that is smaller than the heightof region 420, with regions 410, 415 having intermediate heights.

The respective heights and widths of different regions 405, 410, 415,420, 425, 430, 435, 440 fill a larger percentage of the design space ofan electric motor or generator than can be filled using wires that haveeither a round or other cross section. A cast conductive coil may thusbe advantageous in a number of ways. For example, casting can providerelatively precise control over the dimensions and positioning of metalstrip 310. This allows a relatively large portion of the cross-sectionalarea (such as shown in FIG. 4) to be filled with conductive metal. Byway of comparison, coils formed from a wire that has a circularcross-section necessarily includes larger gaps where current is notconducted. As a result, the maximum current density per cross-sectionalarea is reduced, as is, e.g., the strength of the magnetic field thatcan be generated and the power density of a motor.

Also, since metal strip 310 contacts itself in adjacent layers 312 overa relatively large area, heat can be transferred relatively efficientlyacross coil 300. This is beneficial, e.g., in applications where currentdensity is relatively high and the heat from resistive heating is to beconducted away from coil 300.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade. For example, other products, including, e.g., vehicle suspensionsystems, tire rims, an structural parts can be cast. As another example,rather than casting molten metal 135, salts or salt mixtures can becast. Cast salts can be used, e.g., as cores in high pressure diecasting.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method for casting metals or salts, the methodcomprising: evacuating a mold that is pressurized with an inert gas andcoupled to a pressurized source of molten metal or salt, wherein thepressurization of the source is sufficiently high to drive the moltenmetal or salt into the mold in response to the evacuation.
 2. The methodof claim 1, wherein evacuating the mold comprises coupling the mold to avacuum chamber, wherein the vacuum chamber has a volume that is 10 to100 time a volume of the mold.
 3. The method of claim 1, wherein thesource of molten metal or salt is pressurized to a pressure of less than0.2 MPa gage or less.
 4. The method of claim 1, wherein the source ofmolten metal or salt is pressurized with the inert gas.
 5. The method ofclaim 1, wherein the mold is configured to cast a coil.
 6. The method ofclaim 1, wherein the mold is evacuated in 0.1 seconds or less.
 7. Themethod of claim 1, wherein: prior to the evacuation, the pressurizationof the interior of the mold and the pressurization of the source arecomparable and molten metal or salt is exposed to the inert gaspressurizing the mold.
 8. The method of claim 1, further comprising:during the evacuation, after the evacuation, or both during and afterthe evacuation, increasing pressurization of the source of molten metalor salt.
 9. The method of claim 1, wherein the mold comprises a core,multiple slides, or both a core and multiple slides.
 10. The method ofclaim 9, wherein the mold comprises a gas-permeable core and whereinevacuating the mold comprises evacuating at least part of the mold bydrawing gas through the gas-permeable core.
 11. The method of claim 1,wherein the pressurized source comprises a crucible that includesresistive or inductive heating elements integrated therein or disposedalong a surface thereof.
 12. A coil comprising: a cast unitary metalstrip covered by an insulator and layered to form a plurality of turnsabout an axis, the metal strip having a width generally perpendicular tothe axis and a height generally parallel to the axis, wherein the widthis larger than the height.
 13. The coil of claim 12, wherein the castunitary metal strip has a generally rounded rectangular cross-sectionparallel to the axis.
 14. The coil of claim 12, wherein the insulationof adjacent turns of the metal strip contact each other oversubstantially the entire width of the metal strip.
 15. The coil of claim12, wherein the coil displays physical characteristics that arecharacteristic being cast in a relatively low pressure differencecasting process.
 16. The coil of claim 15, wherein the physicalcharacteristics include dimensions of microbubbles in the coil.
 17. Thecoil of claim 12, wherein the coil displays physical characteristicsthat are characteristic being cast directly in a shape that is nearlysuitable for use, for example, wherein the metal strip is free fromstress-induced microdefects resulting from an application of a forceperpendicular to the axis to shape the metal strip.
 18. The coil ofclaim 12, wherein the metal strip comprises aluminum and the insulatorcomprises aluminum oxide.
 19. The coil of claim 12, wherein the castunitary metal strip coil has a generally trapezoidal cross sectionparallel to the axis, wherein the cross section is oriented to intersectcomparable cross sections of other coils of a motor or generatorarranged generally concentrically about a center.
 20. The coil of claim20, wherein the generally trapezoidal cross section is formed by asingle winding of the cast unitary metal strip.
 21. The coil of claim12, wherein, in at least one cross section parallel to the axis, regionsof the cast unitary metal strip have non-uniform widths.
 22. The coil ofclaim 21, wherein the regions progressively increase or decrease inwidth along the axis.
 23. The coil of claim 21, wherein, in the at leastone cross section parallel to the axis, regions of the cast unitarymetal strip have non-uniform heights, for example, wherein the regionsprogressively increase or decrease in height along the axis.
 24. Thecoil of claim 12, wherein the coil is cast in an extended shape thatforms a plurality of turns about an axis with a space between adjacentturns, for example, wherein the space between adjacent turns is 5 to 10times wider than the thickness of the metal strip along the axis.